1. Field of the Invention
The present invention relates to a surface acoustic wave (hereinafter referred to as SAW in abbreviation) device, particularly to structure of a SAW device such as a SAW filter for use in mobile communication equipment.
2. Description of Related Art
Recently, with development of mobile communication systems, portable phones, portable information terminals and the like have been getting widespread rapidly. Miniaturization of such terminal equipment with improved performance is under active research and development. Now, both an analog system and a digital system are in use for portable phones, and their radio frequency in use covers wide bands from 800 MHz to 1 GHz and from 1.5 GHz to 2.0 GHz, and their intermediate frequency in use from 40 MHz to 400 MHz as usual.
In conventional SAW filters, a filter circuit having desired pass characteristics is formed on one chip. The chip is accommodated in one package.
In recent years, however, communication systems of various types are put into practice in the field of mobile communication technology. As a result, a terminal is required to be compatible with a plurality of systems. Accordingly, the development of circuits and terminals capable of plural systems has now become vigorous, and dual SAW filters are becoming in use. For example, SAW devices have been developed which are so constructed that two SAW filter circuits are formed on one chip which is then accommodated in one package or that two filters each with one SAW filter circuit formed thereon are accommodated in one package and the like.
In such circumstances, for the development of SAW filters compatible with more and more diversified systems, a SAW filter package should be designed to accommodate as many SAW filter chips as possible therein.
In some cases, one package needs to accommodate several SAW filters having different parameters. The parameters include center frequency, pass band width and the like.
Further, it is required to consider whether external output/input terminals should be of balanced type or of unbalanced type, whether one package should accommodate SAW filters having input/output terminals of both types or the like.
As the number of SAW filter chips increases, external connection terminals for input and output on the plural SAW filter chips are connected with many terminals for connection mounted on the package accommodating the filter chips, in much more complicated way.
For example, conventionally, the connection terminals mounted on the package are connected with the external connection terminals on the filter chips by wire bonding, i.e., the terminals are directly connected by aerial wiring using a lot of metallic wires. The connection terminals on the package must be arranged in such a manner that these wires do not contact each other. This complication in arranging the connection terminals may result in a decline in productivity, limitations in designing the connection terminals on the package and electrodes formed on the filter chip and the like.
Further, where the connection terminals on the package are connected with the external connection terminals on the filter chips by wire bonding, there rise such problems that unnecessary radio wave may be generated from the wires (aerial wiring), that resistance of the wires or the like may affect characteristics of the SAW filter, and especially, that an attenuation characteristic out of the pass band may decline.